Image processing apparatus and image processing method

ABSTRACT

Image processing apparatus and image processing method for formation of high quality image by high-speed error diffusion processing by execution of more complicated threshold condition processing in a simple manner. When error diffusion processing is performed on multivalued image data having plural density components and the result of processing is outputted, upon execution of error diffusion processing on a first density component among the plural density components, a threshold value used in the error diffusion processing is determined based on a density value of a second density component, then the error diffusion processing is performed on the first density component based on the determined threshold value, and the result of execution of the error diffusion processing is outputted. Further, upon execution of the error diffusion processing on the second density component among the plural density components, a threshold value used in the error diffusion processing is determined based on a density value of the first density component, then the error diffusion processing is performed on the second density component based on the determined threshold value, and the result of the error diffusion processing is outputted.

FIELD OF THE INVENTION

The present invention relates to an image processing apparatus and an image processing method, and more particularly, to an image processing apparatus and an image processing method for pseudo-halftoning by performing error diffusion processing on multivalued image density data.

BACKGROUND OF THE INVENTION

Conventionally, the error diffusion method is known as pseudo-halftoning to represent a multivalued image in binary representation (See “An Adaptive Algorithm for Spatial Gray Scale” in Society for Information Display 1975 Symposium Digest of Technical Papers, 1975, pp. 36). According to this method, assuming that a pixel of interest is P and its density is v, densities of adjacent pixels P0 to P3 of the pixel of interest P, v0 to v3, and a threshold value for binarization is T, a binarization error E in the pixel of interest P is distributed by empirically obtained weighting coefficients W0 to W3 into the adjacent pixels P0 to P3 so that a mean density is macroscopically equal to an original image density.

For example, when the value of output binary data is “o”, If v≧T holds, o=1, E=v−Vmax;  (1)

-   -   If v<T holds, o=0, E=v−Vmin;     -   (Vmax: maximum density, Vmin: minimum density)         v0=v0+E×W0;  (2)         v1=v1+E×W1;  (3)         v2=v2+E×W2;  (4)         v3=v3+E×W3;  (5)

(Example of weighting coefficients: W0= 7/16, W1= 1/16, W2= 5/16, W3= 3/16)

Conventionally, when a multivalued image is outputted by a color ink-jet printer or the like using 4 color inks of cyan (C), magenta (M), yellow (Y) and black (K), the pseudo-halftoning is performed by using the error diffusion method or the like for each color. Regarding each color, the processing provides an excellent visual characteristic, however, regarding overlapped two or more colors, does not always provide such a excellent visual characteristic.

To solve this problem, Japanese Published Unexamined Patent Application Nos. Hei 8-279920 and Hei 11-10918 disclose halftoning to obtain an excellent visual characteristic even in overlapped two or more colors by using the error diffusion method for combination of two or more colors.

Further, Japanese Published Unexamined Patent Application No. Hei 9-139841 discloses similar improvement by performing pseudo-halftoning independently on two or more colors and then correcting output values by the sum of input values.

Especially, to reduce graininess of intermediate density area of color image, it is effective to perform image formation avoiding overlap between cyan (C) component and magenta (M) component, and for this purpose, the following method is employed.

FIG. 24 shows image formation control according to a conventional ink-jet method.

In this figure, image data is multivalue data where each density component (YMCK) of each pixel is represented as 8-bit data (0–255 gray-scale value).

Assuming that densities of C and M components of original image are C and M, densities Ct and Mt of the C and M components of pixel of interest in the multivalue color image are represented as follows.

-   -   Ct=C+Cerr     -   Mt=M+Merr         Cerr and Merr are error-diffused values of the C and M         components with respect to the pixel of interest.

As shown in FIG. 24, regarding C and M image formation, 4 types of image formation controls are performed in accordance with the densities of the C and M components of the pixel of interest.

-   1. If the sum of (Ct+Mt) is equal to or less than a threshold value     (Threshold1), i.e., the value belongs to an area (1) in FIG. 24, dot     printing is not performed using C or M inks. -   2. If the sum of (Ct+Mt) is greater than the threshold value     (Threshold1) and the sum of (Ct+Mt) is less than another threshold     value (Threshold2), and Ct>Mt holds, i.e., the value belongs to an     area (2) in FIG. 24, dot printing using only the C ink is performed. -   3. If the sum of (Ct+Mt) is greater than the threshold value     (Threshold1) and the sum of (Ct+Mt) is less than the other threshold     value (Threshold2), and Ct≦Mt holds, i.e., the value belongs to an     area (3) in FIG. 24, dot printing is performed using only the M ink. -   4. If the sum of (Ct+Mt) is equal to or greater than the other     threshold value (Threshold2), i.e., the value belongs to an area (4)     in FIG. 24, dot printing is performed using the C and M inks.

Note that Threshold1<Threshold2 holds.

However, in the above conventional art, as the image formation for the C and M components differs in accordance with the sum of the density values of the C and M components, the image formation control must be simple. If pixels where image data to be processed changes prior near a threshold value are adjacent to each other, a pixel where the C ink and the M ink overlap with each other and a pixel where these inks do not overlap with each other mixedly appear in the narrow area, and as a result, the quality of image formation is degraded.

To prevent the degradation of image quality, more complicated thresholds may be employed. However, the threshold condition processing must be more complicated, and processing time is prolonged.

Further, since the conventional threshold processing must be inevitably simple in the processing based on the sum of the density values of the C and M components, flexible processing cannot be performed without difficulty.

Further, if exclusive error diffusion is to be performed by using the sum of three components including the black (K) component, the processing becomes very complicated as represented in the following code.

Ct=C+Cerr Mt=M+Merr Kt=K+Kerr If (Ct+Mt+Kt>Threshold1) If (Ct+Nt+Kt<Threshold2) If (Ct>Mt&&Ct>Kt) Print C Else If (Mt>Ct&&Mt>Kt) Print M Else Print K Else If (Ct+Mt+Kt<Threshold 3) If (Ct<Mt&&Ct>Kt) Print M Print K Else If (Mt<Ct&&Mt<Kt) Print C Print K Else Print C Print M Else Print C Print M Print K

Further, in the above conventional art, the input multivalued image data is merely binarized by each color component and subjected to the error diffusion processing as the pseudo-halftoning. On the other hand, in accordance with the progress of color image printing technology by the ink-jet method, some ink-jet printers can handle multivalued image data for color image printing by drop modulation or use of same-color thick and thin inks.

Accordingly, it is desirable to apply multivalue error diffusion processing to the above ink-jet printer. However, in the multivalue error diffusion processing, as the threshold condition processing is so complicated, if the processing is applied to an actual printer, the reduction of printing speed is conceivable. For this reason, upon application of the multivalue error diffusion processing to an ink-jet printer to handle multivalued image data, a processing method capable of maintaining a high processing speed is desirable.

Further, as in the case of the above conventional art, in image formation by completely and exclusively arranging C component and M component dots, in an original image having respectively 50% C and M component, all the pixels are filled with C ink dots or M ink dots, ideally, as shown in FIG. 25A. In this state, if C-ink dot positions and M-ink dot positions are relatively shifted from each other for some reason as shown in FIG. 25B, the image has pixels where C-ink dot and M-ink dot overlap with each other (bluish pixels) and blank pixels without dot throughout most of the image.

Accordingly, in printing by an ink-jet printer using a printhead where C-ink nozzles and M-ink nozzles are arrayed in a scan direction of a carriage of the printer, a formed image periodically changes in accordance with the position of the carriage in the scan direction by variation in carriage scan speed or the like, as shown in FIGS. 25A and 25B, and it looks to a human eye that the density of corresponding area periodically changes due to the variation in probability of occurrence of blank pixels. In other words, to a human eye, the printed result appears as a low-quality image.

On the other hand, if C-ink dots and M-ink dots are independently arranged in an image formation, in an original image having respectively 50% C and M components as in the above case, blank pixels, pixels printed only with the C ink, pixels printed only with the M ink, and pixels printed with both the C and M inks are formed respectively at 25% occurrence uniformly in the formed image, ideally, as shown in FIG. 26A.

In the independent arrangement of C-ink dots and M-ink dots, a pixel to be printed only with the C ink may overlap with an adjacent pixel to be printed with the M ink, as shown in FIG. 26B, on the other hand, there is a probability that a pixel to be printed with both the C and M inks is printed with only the C ink or the M ink. Thus, the overall density change is small in comparison with the exclusive arrangement of C-ink and M-ink dots.

Accordingly, it is understood that the exclusive arrangement of C-ink and M-ink dots has a problem that the uniformity of image is degraded from intermediate to high density areas in view of a trade-off between the effect of reduction of graininess in a highlight portion and image formation accuracy. If only the highlight portion is taken into consideration, as respective dots are initially arranged sufficiently away from each other, the degradation of image quality due to shift of dot positions is very little and the advantage of the exclusive arrangement is rather greater.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide an image processing apparatus and an image processing method capable of (1) forming a high quality image by performing high-speed error diffusion processing by performing more complicated threshold condition processing in a simple manner; (2) forming a high quality image at a high speed while using multivalue error diffusion processing; and (3) forming a high quality image by performing optimum pixel arrangement in accordance with image density.

According to one aspect of the present invention, the foregoing object is attained by providing an image processing apparatus for performing error diffusion processing on multivalued image data having plural density components and outputting the result of the error diffusion processing, comprising: first determination means for, upon execution of the error diffusion processing on a first density component among the plural density components, determining a threshold value used in the error diffusion processing based on a density value of a second density component; first error diffusion execution means for executing the error diffusion processing on the first density component based on the threshold value determined by the first determination means; first output means for outputting the result of execution of the error diffusion processing by the first error diffusion execution means; second determination means for, upon execution of the error diffusion processing on the second density component among the plural density components, determining a threshold value used in the error diffusion processing based on a density value of the first density component; second error diffusion execution means for performing the error diffusion processing on the second density component based on the threshold value determined by the second determination means; and second output means for outputting the result of execution of the error diffusion processing by the second error diffusion execution means.

It is preferable that the first and second determination means use a table showing a relation between density and threshold values, for determining the threshold values.

It may be arranged such that the first and second determination means respectively determine plural threshold values for N-ary conversion as well as binarization. In this case, it is preferable that the first and second determination means respectively use plural tables for determining the plural threshold values.

Further, it may be arranged such that the apparatus further comprises: third determination means for, upon execution of the error diffusion processing on a third density component among the plural density components, determining a threshold value used in the error diffusion processing based on the sum of the density values of the first and second density components; third error diffusion execution means for executing the error diffusion processing on the third density component based on the threshold value determined by the third determination means; and third output means for outputting the result of execution of the error diffusion processing by the third error diffusion execution means.

In this manner, it is preferable that in a case where the error diffusion processing is performed on the first to third density components, the first determination means determines the threshold value used in the error diffusion processing on the first density component, based on the sum of the density value of the second density component and a density value of the third density component, and the second determination means determines the threshold value used in the error diffusion processing on the second density component, based on the sum of the density value of the first density component and the density value of the third density component.

Note that the plural density components are a yellow component, a magenta component, a cyan component and a black component, and the first density component is the cyan component, the second density component is the magenta component, and the third density component is the black component.

Further, it is preferable that the apparatus further comprises image formation means such as an ink-jet printer for inputting the error diffusion processing results outputted from the first, second and third output means and performing image formation.

It is preferable that the ink-jet printer has an ink-jet printhead that discharges ink by utilizing thermal energy, and the ink-jet printhead has electrothermal transducers for generating the thermal energy to be supplied to the ink.

According to another aspect of the present invention, the foregoing object is attained by providing an image processing method for performing error diffusion processing on multivalued image data having plural density components and outputting the result of the error diffusion processing, comprising: a first determination step of, upon execution of the error diffusion processing on a first density component among the plural density components, determining a threshold value used in the error diffusion processing based on a density value of a second density component; a first error diffusion execution step of executing the error diffusion processing on the first density component based on the threshold value determined at the first determination step; a first output step of outputting the result of execution of the error diffusion processing at the first error diffusion execution step; a second determination step of, upon execution of the error diffusion processing on the second density component among the plural density components, determining a threshold value used in the error diffusion processing based on a density value of the first density component; a second error diffusion execution step of performing the error diffusion processing on the second density component based on the threshold value determined at the second determination step; and a second output step of outputting the result of execution of the error diffusion processing at the second error diffusion execution step.

According to still another aspect of the present invention, the foregoing object is attained by providing a computer readable storage medium for storing a program for executing the above image processing method.

In accordance with the present invention as described above, when error diffusion processing is performed on multivalued image data having plural density components and the result of processing is outputted, upon execution of the error diffusion processing on the first density component among the plural density components, a threshold value to be used in the error diffusion processing is determined based on the density value of the second density component, then the error diffusion processing is executed on the first density component based on the determined threshold value, and the result of execution of the processing is outputted. Further, upon execution of the error diffusion processing on the second density component among the plural density components, a threshold value to be used in the error diffusion processing is determined based on the density value of the first density component, then the error diffusion processing is executed on the second density component based on the determined threshold value, and the result of execution of the processing is outputted.

According to still another aspect of the present invention, the foregoing object is attained by providing an image processing apparatus for performing error diffusion processing on multivalued image data having plural density components and outputting the result of the error diffusion processing, comprising: calculation means for calculating the sum and difference between density values of the first density component and second density component among the plural density components; M-ary conversion means for converting the sum value into M-ary code by using a first function based on the sum; N-value conversion means for converting the difference value into N-ary code by using a second function based on the difference; and execution means for executing multivalue error diffusion processing respectively on the first and second density components, based on the result of conversion by the M-ary conversion means and the result of conversion by the N-ary conversion means.

Note that M and N are respectively a positive integer equal to or greater than 3.

Further, it is preferable that the first function used in the M-ary conversion means is represented in a first table showing a relation between the sum value and an M-ary code, and the second function used in the N-ary conversion means is represented in a second table showing a relation between the difference value and an N-ary code.

Further, it is preferable that the multivalue error diffusion processing is executed by the execution means by using a two-dimensional table with the result of the conversion by the M-ary conversion means and the result of the conversion by the N-ary conversion means as functions. It may be arranged such that the two-dimensional table is a common table for the first and second density components, otherwise, the two-dimensional table is prepared respectively for the first and second density components.

In the above case, the plural density components are a yellow component, a magenta component, a cyan component and a black component, and the first density component is the cyan component, and the second density component is the magenta component.

Further, it is preferable that the apparatus further comprises image formation means such as an ink-jet printer for inputting the error diffusion processing results and performing image formation.

It is preferable that the ink-jet printer has an ink-jet printhead that discharges ink by utilizing thermal energy, and the ink-jet printhead has electrothermal transducers for generating the thermal energy to be supplied to the ink.

According to still another aspect of the present invention, the foregoing object is attained by providing an image processing method for performing error diffusion processing on multivalued image data having plural density components and outputting the result of the error diffusion processing, comprising: a calculation step of calculating the sum and difference between density values of first density component and second density component among the plural density components; an M-ary conversion step of converting the sum value into M-ary code by using a first function based on the sum; an N-ary conversion step of converting the difference value into N-ary code by using a second function based on the difference; and an execution step of executing multivalue error diffusion processing respectively on the first and second density components, based on the result of conversion at the M-ary conversion step and the result of conversion at the N-ary conversion step.

According to still another aspect of the present invention, the foregoing object is attained by providing a computer readable storage medium for storing a program for executing the above image processing method.

In accordance with the present invention as described above, when error diffusion processing is performed on multivalued image data having plural density components and the result of the error diffusion processing is outputted, the sum and the difference between the density value of the first density component and that of the second density component among the plural density components are calculated, the sum value is converted into M-ary code by using the first function based on the sum, while the difference value is converted into N-ary code by using the second function based on the difference. Then multivalue error diffusion processing is performed on the first density component and the second density component based on the results of the M-ary conversion and the N-ary conversion.

According to still another aspect of the present invention, the foregoing object is attained by providing an image processing apparatus for performing error diffusion processing on multivalued image data having plural density components and outputting the result of the error diffusion processing, comprising: analysis means for examining density values of a first density component and a second density component among the plural density components; and control means for exclusively or independently outputting the result of the error diffusion processing on the first density component and that of the error diffusion processing on the second density component, in accordance with the result of analysis by the analysis means, wherein if at least one of the first and second density components has an intermediate density value, the control means independently outputs the results of the error diffusion processing, while if the first and second density components do not have an intermediate density value, exclusively outputs the results of the error diffusion processing.

It may be arranged such that the analysis means includes: first comparison means for comparing the sum of the density values of the first and second density components among the plural density components with a predetermined threshold value; and second comparison means for comparing the density value of the first density component and the density value of the second density component with each other, and that the control means performs printing by the error diffusion processing based on the first density component or the second density component, based on the results of comparison by the first and second comparison means.

Further, it is preferable that the apparatus further comprises third comparison means for comparing the density value of the first density component with the predetermined threshold value, and the control means further determines whether or not printing by the error diffusion processing is to be performed not only based on the first density component, but also based on the result of comparison by the third comparison means.

Otherwise, it is preferable that the apparatus further comprises fourth comparison means for comparing the density value of the second density component with the predetermined threshold value, and the control means further determines whether or not printing by the error diffusion processing is to be performed not only based on the second density component, but also based on the result of comparison by the fourth comparison means.

In the above case, the plural density components are a yellow component, a magenta component, a cyan component and a black component, and the first density component is the cyan component, and the second density component is the magenta component.

It may be arranged such that the plural density components of the multivalued image data are respectively binarized by the error diffusion processing, otherwise, the plural density components of the multivalued image data are respectively converted into N-ary code (N≧3 positive integer) by the error diffusion processing. Further, it may be arranged such that the apparatus further comprises a table showing relation between a density value and an N-ary code output value, for the N-ary conversion. It may be arranged such that the table is a common table for the first and second density components, otherwise, the table is prepared respectively for the first and second density components.

Further, it is preferable that the apparatus further comprises image formation means such as an ink-jet printer for inputting the result of execution of the error diffusion processing and performing image formation.

It is preferable that the ink-jet printer has an ink-jet printhead that discharges ink by utilizing thermal energy, and the ink-jet printhead has electrothermal transducers for generating the thermal energy to be supplied to the ink.

Note that the intermediate density is higher than an approximately half level of a maximum density level.

According to still another aspect of the present invention, the foregoing object is attained by providing an image processing method for performing error diffusion processing on multivalued image data having plural density components and outputting the result of the error diffusion processing, comprising: an analysis step of examining density values of a first density component and a second density component among the plural density components; and a control step of exclusively or independently outputting the result of the error diffusion processing on the first density component and that of the error diffusion processing on the second density component, in accordance with the result of analysis at the analysis step, wherein at the control step, if at least one of the first and second density components has an intermediate density value, the results of the error diffusion processing are independently outputted, while if the first and second density components do not have an intermediate density value, the results of the error diffusion processing are exclusively outputted.

According to still another aspect of the present invention, the foregoing object is attained by providing a computer-readable storage medium holding a program for execution of the above-described image processing method.

In accordance with the present invention as described above, when error diffusion processing is performed on multivalued image data having plural density components and the result of processing is outputted, the density value of the first density component and that of the second density component among the plural density components are examined, and in accordance with the result of analysis, the results of error diffusion processing on the first and second density components are exclusively outputted unless the density components of the first and second density component have intermediate densities, otherwise, independently outputted if at least one of the first and second density components has an intermediate density.

The invention is particularly advantageous since the error diffusion processing is performed in consideration of the value of another density component, image formation in consideration of overlap with another component is possible, and a high quality image can be formed.

Further, as the threshold used in the error diffusion processing is determined by using a table, the error diffusion processing can be performed at a high speed by performing more complicated threshold condition processing in a simple manner.

Further, when error diffusion processing is performed on multivalued image data having plural density components and the result of processing is outputted, the sum and difference between the density value of the first density component and that of the second density component among the plural density components are calculated, and the sum value is converted into M-ary code by using the first function based on the sum, while the difference value is converted into N-ary code by using the second function based on the difference. Then based on the results of M-ary and N-ary conversion, the multivalue error diffusion processing is performed on the first and second density components. Accordingly, complicated threshold condition processing accompanying the multivalue error diffusion processing becomes unnecessary due to representing the first and second functions in the form of table, introducing the tables into the multivalue error diffusion processing, and performing the error diffusion processing by referring to these tables. Thus the multivalue error diffusion processing can be performed at a high speed.

Further, when error diffusion processing is performed on multivalued image data having plural density components and the result of processing is outputted, the density value of the first density component and that of the second density component among the plural density components are examined, and in accordance with the result of analysis, the results of error diffusion processing on the first and second density components are exclusively outputted unless the density components of the first or second density component have intermediate densities, otherwise, independently outputted if at least one of the first and second density components has an intermediate density. Accordingly, the graininess from highlight to intermediate density areas in the image can be reduced, and the uniformity of the image can be maintained from the intermediate to high density areas, thus a high quality image can be formed.

Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same name or similar parts throughout the figures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

FIG. 1 is a block diagram showing a schematic configuration of an information processing system according to a common embodiment of the present invention;

FIG. 2 is a block diagram showing a hardware construction of host device 51 and that of image output device 52 constructing the information processing system;

FIG. 3 is a perspective view of an ink-jet printer IJRA as a typical embodiment of the image output device 52;

FIG. 4 is a block diagram showing a software construction used in the information processing system;

FIG. 5 is a flowchart showing the outline of image processing;

FIG. 6 is a flowchart showing image formation control according to a first embodiment of the present invention;

FIGS. 7A to 7C are diagrams showing threshold conditions used in the first embodiment;

FIGS. 8A to 8C are diagrams showing other threshold conditions used in the first embodiment;

FIGS. 9A to 9D are diagrams showing examples of applicable various threshold conditions;

FIG. 10 is a flowchart showing the image formation control according to a second embodiment of the present invention;

FIGS. 11A to 11C are diagrams showing threshold conditions used in the second embodiment;

FIGS. 12A to 12C are diagrams other threshold conditions used in the second embodiment;

FIG. 13 is a flowchart showing the image formation control according to a third embodiment of the present invention;

FIG. 14 is a flowchart showing the image formation control according to a fourth embodiment of the present invention;

FIG. 15 is a diagram showing threshold conditions used in the fourth embodiment;

FIG. 16 is a flowchart showing the image formation control according to a fifth embodiment of the present invention;

FIG. 17 is a diagram showing threshold conditions used in the fifth embodiment;

FIG. 18 is a diagram showing a two-dimensional common table for C and M components used in the fifth embodiment;

FIGS. 19A to 19B are diagrams showing two-dimensional tables specialized for the C and M components;

FIG. 20 is a flowchart showing the image formation control according to a sixth embodiment of the present invention;

FIG. 21 is a diagram showing threshold conditions used in the sixth embodiment;

FIG. 22 is a flowchart showing the image formation control according to a seventh embodiment of the present invention;

FIG. 23 is a diagram showing threshold conditions used in the seventh embodiment;

FIG. 24 is a diagram showing the image formation control according to the conventional ink-jet method;

FIGS. 25A and 25B are diagrams showing image formation by exclusively arranging the C and M components; and

FIGS. 26A to 26B are diagrams showing image formation by independently arranging the C and M components.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will now be described in detail in accordance with the accompanying drawings.

[Common Embodiment]

First, the outline of a common information processing system used in the following embodiments, the outline of hardware construction, the outline of software construction and the outline of image processing will be described.

FIG. 1 is a block diagram showing a schematic configuration of the information processing system according to a common embodiment of the present invention.

As shown in FIG. 1, the information processing system has a host device 51 comprising a personal computer or the like, and an image output device 52 comprising a printer or the like, interconnected via a bidirectional interface 53. Driver software 54, to which the present invention is applied, is loaded into a memory of the host device 51.

-   1. Hardware Construction of Host Device 51 and Image Output Device     52

Next, the hardware construction of the host device 51 and that of the image output device 52 will be described.

FIG. 2 is a block diagram showing the hardware construction of the host device 51 and that of the image output device 52 constructing the information processing system.

As shown in FIG. 2, the host device 51, having a processor 1000 and its peripheral devices, serves as a host device. Further, the image output device 52 has a driving portion including a printhead 3010, a carrier (CR) motor 3011 to drive a carrier to move the printhead 3010, a linefeed motor 3012 to feed paper and the like, and a control circuit 3013.

The processor 1000 of the host device 51 includes an MPU 1001 which controls the overall operation of the host device in accordance with a control program, a bus 1002 which interconnects system constituent elements, a DRAM 1003 for temporarily storing programs executed by the MPU 1001 and data, a bridge 1004 which connects the system bus, the memory bus and the MPU 1001, and a graphic adapter 1005 having a control function to display graphic information on a display device 2001 such as a CRT.

Further, the processor 1000 has an HDD controller 1006 which serves as an interface between the processor and an HDD device 2002, a keyboard controller 1007 which serves as an interface between the processor and a keyboard 2003, and a communication I/F 1008 as a parallel interface for communication between the processor and the image output device 52 according to the IEEE 1284 standards.

Further, the processor 1000 is connected, via the graphic adapter 1005, to the display device 2001 (CRT in this embodiment) which displays graphic information and the like for an operator. Further, the processor 1000 is connected, via respective controllers, to the hard disk drive (HDD) device 2002 as a large capacity storage device holding programs and data and the keyboard 2003.

On the other hand, the control circuit 3013 of the image output device 52 has an MCU 3001, having a control program execution function and a peripheral device control function, which controls the overall operation of the image output device main body 52, a system bus 3002 which interconnects the respective constituent elements of the control circuit, and a gate array (G.A.) 3003 including mechanisms to supply print data to the printhead 3010, to perform memory address decoding, and to generate a control pulse to the carrier motor and the like, as a control circuit.

Further, the control circuit 3013 has a ROM 3004 for storing the control programs executed by the MCU 3001, host print information and the like, a DRAM 3005 for storing various data (image print information, print data to be supplied to the printhead and the like), a communication I/F 3006 as a parallel interface for communication between the control circuit and the host device 51 according to the IEEE 1284 standards, and a head driver 3007 which converts a head print signal outputted from the gate array 3003 into an electric signal to drive the printhead 3010.

Further, the control circuit 3013 has a CR motor driver 3008 which converts the carrier motor control pulse outputted from the gate array 3003 into an electric signal to actually drive the carrier (CR) motor 3011, and an LF motor driver 3009 which converts a linefeed motor control pulse outputted from the MCU 3001 into an electric signal to actually drive the linefeed motor.

Next, a particular structure of the image output device 52 will be described.

FIG. 3 is a perspective view of an ink-jet printer IJRA as a typical embodiment of the image output device 52.

In FIG. 3, a carriage HC is engaged with a spiral groove 5004 of a lead screw 5005 which rotates via drive force transmission gears 5009 to 5011 interlocking with forward/reverse rotation of a driving motor 5013. The carriage HC has a pin (not shown) and it reciprocates in directions indicated by arrows a and b, held by a guide rail 5003. The carriage HC has an ink-jet cartridge IJC which integrally comprises a printhead IJH and an ink tank IT. A paper holding plate 5002 presses a print sheet P against a platen 5000 along the moving direction of the carriage HC. Photocouplers 5007 and 5008 are home position detecting members for checking the existence of lever 5006 of the carriage in this area and changing over the rotational direction of the motor 5013. A support member 5016 supports a cap member 5022 for capping the front surface of the printhead IJH. A suction member 5015 performs suction-recovery of the printhead by sucking the inside of the cap member 5022 via a cap inner opening 5023. Member 5019 allows a cleaning blade 5017 to move in back-and-forth directions. A main body support plate 5018 supports the member 5019 and the cleaning blade 5017. It is apparent that any well-known cleaning blade is applicable to the printer of the embodiment. Numeral 5021 denotes a lever for starting the sucking operation of the suction-recovery. The lever 5021 moves along the movement of a cam 5020 engaged with the carriage HC. A well-known transmission mechanism such as clutch change over controls a drive force from the driving motor.

When the carriage HC is at the home position area, a desired one of these capping, cleaning and suction-recovery is executed at its corresponding position by the lead screw 5005. The timing of any of these processings is not limited to the printer of the embodiment, if a desired processing is performed at a well-known timing.

Note that as described above, the ink tank IT and the printhead IJH may be integrally formed as an exchangeable ink cartridge IJC. Further, it may be arranged such that the ink tank IT and the printhead IJH can be separated, and when ink is exhausted, only the ink tank IT is exchanged for new one.

Further, the control circuit described above with reference to FIG. 2 is included in the ink-jet printer IJRA.

The printhead IJH prints a color image by using at least four color inks of yellow (Y), magenta (M), cyan (C) and black (K) based on multivalued density data of respective YMCK components.

-   2. Outline of Software Construction and Outline of Image Processing

FIG. 4 is a block diagram showing the software construction used in the above-described information processing system.

As it is understood from FIG. 4, to output print data to the image output device 52, the host device 51 performs image processing by collaborated operation among application software, an operating system and driver software in a layer structure.

In the present embodiment, processings individually depending on the image output devices are handled by device-specific drawing functions 31-1, 31-2, . . . , 31-n, separated from a program for generally executing programs depending on individual implementations of image processing apparatus. Further, the core processing of driver software is independent of the individual image output devices.

A line-segmented image converted into a quantized amount is subjected to image processing by a color characteristic conversion module 33, a halftoning module 34 and the like. Further, a print command generation module 35 adds a command to the data and compresses the data, and delivers the generated data to the image output device 52 via a spooler 22 provided in the OS (Operating System).

As shown in FIG. 4, application software 11 is provided in the layer of application software, and a drawing processing interface 21 which receives a drawing command from the application software 11 and the spooler 22 which delivers the generated image data to the image output device 52 such as an ink-jet printer are provided in the layer of the OS (Operating System).

Then, the device-specific drawing functions 31-1, 31-2, . . . , 31-n holding representation formats specific to the image output devices, the color characteristic conversion module 33 which receives line-segmented image information from the OS and which converts the color representation in the driver to a device-specific color representation, a halftoning module 34 which performs conversion to quantized amounts for representing respective pixel states of the device, and the print command generation module 35 which adds a command to the image output device 52 to the halftoning-processed image data, and outputs the data to the spooler 22, are provided in the layer of driver software.

Next, a particular example of image output from the application software to the image output device 52 will be described with reference to the flowchart of FIG. 5 showing the outline of the image processing together with FIG. 4.

When the application software 11 outputs an image to the image output device 52, first, the application software 11 issues drawing commands to draw character(s), line(s), figure(s), bitmap(s) and the like, through the drawing processing interface 21 of the OS (step S1).

When the drawing commands for constructing an image frame/printing area have been completed (step S2), the OS converts the respective drawing commands in the internal format of the OS into a device-specific representation format (line-segmentation of respective drawing unit information) while calling the device-specific drawing functions 31-1, 31-2, . . . , 31-n inside the driver software (step S3), thereafter, delivers the image information line-segmented from the image frame/printing area to the driver software (step S4).

Inside the driver software, the color characteristic conversion module 33 corrects the color characteristic of the device, and converts the color representation inside the driver software to that specific to the device (step S5), further, the halftoning module 34 performs conversion (halftoning) to a quantized amounts for representing respective pixel states of the device (step S6). Note that the conversion to quantized amount here corresponds to the form of data processed by the image output device 52. If printing by the image output device is performed based on e.g. binary data, binarization is performed, and if printing by the image output device is performed based on multivalue data (for printing by using thick/thin inks and printing by using large-sized and small-sized ink droplets), the data is N-ary-converted.

The details of the halftoning will be described in the subsequent embodiments.

The print command generation module 35 receives quantized (binarized/N-ary-converted) image data (step S7). The print command generation module 35 processes the quantized image information in correspondence with the characteristic of the image output device by different methods. Further, the print command generation module 35 compresses the data and adds a command header to the data (step S8).

Thereafter, the print command generation module 35 forwards the generated data to the spooler 22 provided in the OS (step S9), to output the data to the image output device 52 (step S10).

Note that in the present embodiment, the above-described control method is realized by storing a program according to the flowchart of FIG. 5 into the storage device of the host device 51 and executing the program.

As described above, as the core processing of the driver software is independent of individual image output devices, the distribution of data processing between the driver software and the image output device can be flexibly changed without impairing the construction of the driver software. This is advantageous in view of maintenance and management of the software.

Next, several embodiments using the system according to the above-described common embodiment will be described. In the following embodiments, the details of error diffusion processing performed by the halftoning module 34 will be described.

Note that the error diffusion processing to be described below handles multivalued image data where respective pixels are represented by respectively 8-bit (256 level representation) density data of yellow (Y) component, magenta (M) component, cyan (C) component and black (K) component.

[First Embodiment]

In this embodiment, error diffusion processing, different from the error diffusion processing of the conventional art, capable of complicated threshold condition processing will be described. The processing handles C and M component multivalued image data.

In the present embodiment, multivalued density data is binarized by the error diffusion processing.

FIG. 6 is a flowchart showing image formation control according to the first embodiment of the present invention.

Hereinbelow, the feature of the present embodiment will be described with reference to the flowchart.

First, at step S10, the density values Ct and Mt of the C and M components of pixel of interest are obtained as in the case of the conventional art. Next, at step S20, a threshold value (C threshold) used in error diffusion of the C component is obtained based on the obtained M component density value Mt. More specifically, in this embodiment, threshold tables as shown in Tables 1 and 2 are prepared in the HDD 2002 or the DRAM 1003 of the host device 52 in advance, and the threshold value is determined by referring to the threshold tables.

At step S30, the threshold value (C threshold) obtained at step S20 is compared with the density value Ct of the pixel of interest. If Ct≧C threshold holds, the process proceeds to step S40, at which setting is made for printing with C ink. Thereafter, the process proceeds to step S50. On the other hand, if Ct<C threshold holds at step S30, process skips step S40 and proceeds to step S50.

At step S50, a threshold value (M threshold) used in error diffusion of the M component is obtained based on the obtained C component density value Ct. More specifically, in this embodiment, the threshold tables as shown in Tables 1 and 2 are prepared in the HDD 2002 or the DRAM 1003 of the host device 52 in advance, and the threshold value is determined by referring to the threshold tables.

Accordingly, in this embodiment, both of the threshold tables as shown in Tables 1 and 2 are commonly used for the C component and the M component.

At step S60, the threshold value (M threshold) obtained at step S50 is compared with the density value Mt of the pixel of interest. If Mt≧M threshold holds, the process proceeds to step S70, at which setting is made for printing with M ink. Thereafter, the process ends. On the other hand, if Mt<M threshold holds at step S60, process skips step S70 and the proceeds ends.

Thus, by execution of the above processing, complicated threshold setting can be made only by defining threshold tables having a common format and setting different values in the tables, in the threshold condition processing as shown in FIG. 7A similar to the threshold processing according to the conventional art described in FIG. 24, and further, in the threshold condition processing as shown in FIG. 8A with threshold conditions more complicated than those in FIG. 7A.

Table 1 is a threshold table having threshold conditions corresponding to FIG. 7A, and Table 2, a threshold table having threshold conditions corresponding to FIG. 8A.

TABLE 1 THRESHOLD THRESHOLD THRESHOLD THRESHOLD DENSITY VALUE DENSITY VALUE DENSITY VALUE DENSITY VALUE 0 128 64 64 128 128 192 191 1 127 65 65 129 129 193 190 2 126 66 66 130 130 194 189 3 125 67 67 131 131 195 188 4 124 68 68 132 132 196 187 5 123 69 69 133 133 197 186 6 122 70 70 134 134 198 185 7 121 71 71 135 135 199 184 8 120 72 72 136 136 200 183 9 119 73 73 137 137 201 182 10 118 74 74 138 138 202 181 11 117 75 75 139 139 203 180 12 116 76 76 140 140 204 179 13 115 77 77 141 141 205 178 14 114 78 78 142 142 206 177 15 113 79 79 143 143 207 176 16 112 80 80 144 144 208 175 17 111 81 81 145 145 209 174 18 110 82 82 146 146 210 173 19 109 83 83 147 147 211 172 20 108 84 84 148 148 212 171 21 107 85 85 149 149 213 170 22 106 86 86 150 150 214 169 23 105 87 87 151 151 215 168 24 104 88 88 152 152 216 167 25 103 89 89 153 153 217 166 26 102 90 90 154 154 218 165 27 101 91 91 155 155 219 164 28 100 92 92 156 156 220 163 29 99 93 93 157 157 221 162 30 98 94 94 158 158 222 161 31 97 95 95 159 159 223 160 32 96 96 96 180 160 224 159 33 95 97 97 161 161 225 168 34 94 98 98 162 162 226 157 35 93 99 99 163 163 227 156 36 92 100 100 164 164 228 155 37 91 101 101 165 165 229 154 38 90 102 102 168 166 230 153 39 89 103 103 167 167 231 152 40 88 104 104 168 168 232 151 41 87 105 105 169 169 233 150 42 86 106 106 170 170 234 149 43 85 107 107 171 171 235 148 44 84 108 108 172 172 236 147 45 83 109 109 173 173 237 146 46 82 110 110 174 174 238 145 47 81 111 111 175 175 239 144 48 80 112 112 176 176 240 143 49 79 113 113 177 177 241 142 50 78 114 114 178 178 242 141 51 77 115 115 179 179 243 140 52 76 116 116 180 180 244 139 53 75 117 117 181 181 245 138 54 74 118 118 182 182 246 137 55 73 119 119 183 183 247 136 58 72 120 120 184 184 248 135 57 71 121 121 185 185 249 134 58 70 122 122 186 186 250 133 59 69 123 123 187 187 251 132 60 68 124 124 188 188 252 131 61 67 125 125 189 189 253 130 62 66 126 126 190 190 254 129 63 65 127 127 191 191 255 128

TABLE 2 THRESHOLD THRESHOLD THRESHOLD THRESHOLD DENSITY VALUE DENSITY VALUE DENSITY VALUE DENSITY VALUE 0 128 64 64 128 128 192 128 1 127 65 65 129 128 193 128 2 126 66 66 130 128 194 128 3 125 67 67 131 128 195 128 4 124 68 68 132 128 196 128 5 123 69 69 133 128 197 128 6 122 70 70 134 128 198 128 7 121 71 71 135 128 199 128 8 120 72 72 136 128 200 128 9 119 73 73 137 128 201 128 10 118 74 74 138 128 202 128 11 117 75 75 139 128 203 128 12 116 76 76 140 128 204 128 13 115 77 77 141 128 205 128 14 114 78 78 142 128 206 128 15 113 79 79 143 128 207 128 16 112 80 80 144 128 208 128 17 111 81 81 145 128 209 128 18 110 82 82 146 128 210 128 19 109 83 83 147 128 211 128 20 108 84 84 148 128 212 128 21 107 85 85 149 128 213 128 22 106 86 86 150 128 214 128 23 105 87 87 151 128 215 128 24 104 88 88 152 128 216 128 26 103 89 89 153 128 217 128 26 102 90 90 154 128 218 128 27 101 91 91 155 128 219 128 28 100 92 92 156 128 220 128 29 99 93 93 157 128 221 128 30 98 94 94 158 128 222 128 31 97 95 95 159 128 223 128 32 96 96 96 160 128 224 128 33 95 97 97 161 128 225 128 34 94 98 98 162 128 226 128 35 93 99 99 163 128 227 128 36 92 100 100 164 128 228 128 37 91 101 101 165 128 229 128 38 90 102 102 166 128 230 128 39 89 103 103 167 128 231 128 40 88 104 104 188 128 232 128 41 87 105 105 169 128 233 128 42 86 106 106 170 128 234 128 43 85 107 107 171 128 235 128 44 84 108 108 172 128 236 128 45 83 109 109 173 128 237 128 46 82 110 110 174 128 238 128 47 81 111 111 175 128 239 128 48 80 112 112 176 128 240 128 49 79 113 113 177 128 241 128 50 78 114 114 178 128 242 128 51 77 115 115 179 128 243 128 52 76 116 116 180 128 244 128 53 75 117 117 181 128 245 128 54 74 118 118 182 128 246 128 55 73 119 119 183 128 247 128 56 72 120 120 184 128 248 128 57 71 121 121 185 128 249 128 58 70 122 122 186 128 250 128 59 69 123 123 187 128 251 128 60 68 124 124 188 128 252 128 61 67 125 125 189 128 253 128 62 66 126 126 190 128 254 128 63 65 127 127 191 128 255 128

For example, in a case where the threshold condition processing as shown in FIG. 7A is performed in accordance with the present embodiment, first, at steps S20 to S40, the threshold condition processing as shown in FIG. 7B is performed, then at steps S50 to S70, the threshold condition processing as shown in FIG. 7C is performed.

Similarly, in a case where the threshold condition processing as shown in FIG. 8A is performed in accordance with the present embodiment, first, at steps S20 to S40, the threshold condition processing as shown in FIG. 8B is performed, then at steps S50 to S70, the threshold condition processing as shown in FIG. 8C is performed.

Accordingly, in the above-described embodiment, as the threshold condition processing is performed by using a predetermined format threshold table, even if the threshold conditions are complicated as shown in FIGS. 9A to 9D, the processing can be performed in a simple manner, and as the processing is simple, the complicated threshold condition processing can be performed at a high speed.

[Second Embodiment]

In the first embodiment, the multivalued density data is binarized by the error diffusion processing; in the present embodiment, multivalued density data is ternarized by the error diffusion processing.

FIG. 10 is a flowchart showing the image formation control according to the second embodiment of the present invention.

Hereinbelow, the feature of the present embodiment will be described with reference to the flowchart.

First, at step S100, the density values Ct and Mt of the C and M components of the pixel of interest are obtained as in the case of the conventional art. Next, at step S110, two threshold values (C threshold1 and C threshold2) used in error diffusion of the C component are obtained based on the obtained M component density value Mt. More specifically, in this embodiment, the threshold tables as shown in Tables 3 to 6 are prepared in the HDD 2002 or the DRAM 1003 of the host device 52 in advance, and the threshold values are determined by referring to the threshold tables.

At step S120, one of the threshold values (C threshold1) obtained at step S110 is compared with the density value Ct of the pixel of interest. If Ct≧C threshold1 holds, the process proceeds to step S130, at which the other threshold value (C threshold2) obtained at step S110 is compared with the density value Ct of the pixel of interest. If Ct≧C threshold2 holds, the process proceeds to step S140, at which setting is made for printing by discharging large ink droplets using the C ink. Thereafter, the process proceeds to step S160. On the other hand, if Ct<C threshold2 holds at step S130, the process proceeds to step S150, at which setting is made for printing by discharging small ink droplets using the C ink. Thereafter, the process proceeds to step S160.

Further, if Ct<C threshold1 holds at step S120, the process skips steps S130 to S150 and proceeds to step S160.

At step S160, two threshold values (M threshold1 and M threshold2) used in error diffusion of the M component are obtained based on the obtained C component density value Ct. More specifically, in this embodiment, the threshold tables as shown in Tables 3 to 6 are prepared in the HDD 2002 or the DRAM 1003 of the host device 52 in advance, and the threshold values are determined by referring to the threshold tables.

Accordingly, in this embodiment, the threshold tables in Tables 3 to 6 are commonly used for the C component and the M component.

At step S170, one of the threshold values (M threshold1) obtained at step S160 is compared with the density value Mt of the pixel of interest. If Mt≧M threshold1 holds, the process proceeds to step S180, at which the other threshold value (M threshold2) obtained at step S160 is compared with the density value Mt of the pixel of interest. If Mt≧M threshold2 holds, the process proceeds to step S190, at which setting is made for printing by discharging large ink droplets using the M ink. Then, the process ends. On the other hand, if Mt<M threshold2 holds at step S180, the process proceeds to step S200, at which setting is made for printing by discharging small ink droplets using the M ink. Then the process ends.

On the other hand, if Mt<M threshold1 holds at step S170, the process skips steps S180 to S200 and the process ends.

Thus, by execution of the above processing, complicated threshold setting can easily be made only by defining threshold tables having a common format and setting different values in the tables, in the threshold condition processing as shown in FIG. 11A, and further, in the threshold condition processing as shown in FIG. 12A.

Tables 3 and 4 are threshold tables having threshold conditions corresponding to FIG. 11A, and Tables 5 and 6, threshold tables having threshold conditions corresponding to FIG. 12A.

TABLE 3 THRESHOLD THRESHOLD THRESHOLD THRESHOLD DENSITY VALUE DENSITY VALUE DENSITY VALUE DENSITY VALUE 0 85 64 64 128 43 192 107 1 84 65 65 129 44 193 108 2 83 66 66 130 45 194 109 3 82 67 67 131 46 195 110 4 81 68 68 132 47 196 111 5 80 69 69 133 48 197 112 6 79 70 70 134 49 198 113 7 78 71 71 135 50 199 114 8 77 72 72 136 51 200 115 9 76 73 73 137 52 201 116 10 75 74 74 138 53 202 117 11 74 75 75 139 54 203 118 12 73 76 76 140 55 204 119 13 72 77 77 141 56 205 120 14 71 78 78 142 57 206 121 15 70 79 79 143 58 207 122 16 69 80 80 144 59 208 123 17 68 81 81 145 60 209 124 18 67 82 82 146 61 210 125 19 66 83 83 147 62 211 126 20 65 84 84 148 63 212 127 21 64 85 85 149 64 213 127 22 63 86 84 150 65 214 126 23 62 87 83 151 68 215 125 24 61 88 82 152 67 216 124 25 60 89 81 153 68 217 123 26 59 90 80 154 69 218 122 27 58 91 79 155 70 219 121 28 57 92 78 156 71 220 120 29 56 93 77 157 72 221 119 30 55 94 76 158 73 222 118 31 54 95 75 159 74 223 117 32 53 96 74 160 75 224 116 33 52 97 73 161 76 225 115 34 51 98 72 162 77 226 114 35 50 99 71 163 78 227 113 36 49 100 70 164 79 228 112 37 46 101 69 165 80 229 111 38 47 102 68 166 81 230 110 39 46 103 67 167 82 231 109 40 45 104 66 168 83 232 108 41 44 105 65 169 84 233 107 42 43 106 64 170 85 234 106 43 43 107 63 171 86 235 105 44 44 108 62 172 87 236 104 45 45 109 61 173 88 237 103 46 46 110 60 174 89 236 102 47 47 111 59 175 90 239 101 46 46 112 58 176 91 240 100 49 49 113 57 177 92 241 99 50 50 114 56 178 93 242 98 51 51 115 55 179 94 243 97 52 52 116 54 180 95 244 96 53 53 117 53 181 96 245 95 54 54 118 52 182 97 246 94 55 55 119 51 183 98 247 93 56 56 120 50 184 99 246 92 57 57 121 49 185 100 249 91 58 58 122 48 186 101 250 90 59 59 123 47 187 102 251 89 60 60 124 46 188 103 252 88 61 61 125 45 189 104 253 87 62 62 126 44 190 105 254 86 63 63 127 43 191 106 255 85

TABLE 4 THRESHOLD THRESHOLD THRESHOLD THRESHOLD DENSITY VALUE DENSITY VALUE DENSITY VALUE DENSITY VALUE 0 170 64 149 128 212 192 192 1 169 65 150 129 211 193 193 2 168 66 151 130 210 194 194 3 167 67 152 131 209 195 196 4 166 68 153 132 208 196 196 5 185 69 154 133 207 197 197 6 164 70 155 134 206 198 198 7 163 71 156 135 205 199 199 8 162 72 157 136 204 200 200 9 161 73 158 137 203 201 201 10 160 74 159 138 202 202 202 11 159 75 160 139 201 203 203 12 158 76 161 140 200 204 204 13 157 77 162 141 199 205 205 14 156 78 163 142 198 206 206 15 155 79 164 143 197 207 207 16 154 80 165 144 196 208 208 17 153 81 166 145 195 209 209 18 152 82 167 146 194 210 210 19 151 83 168 147 193 211 211 20 150 84 169 148 192 212 212 21 149 85 170 149 191 213 212 22 148 86 171 150 190 214 211 23 147 87 172 151 189 215 210 24 146 88 173 152 188 216 209 25 145 89 174 153 187 217 208 26 144 90 175 154 186 218 207 27 143 91 176 155 185 219 206 28 142 92 177 156 184 220 205 29 141 93 178 157 183 221 204 30 140 94 179 158 182 222 203 31 139 95 180 159 181 223 202 32 138 96 181 160 180 224 201 33 137 97 182 161 179 225 200 34 136 98 183 162 178 226 199 35 135 99 184 163 177 227 198 36 134 100 185 164 176 228 197 37 133 101 186 165 175 229 196 38 132 102 187 166 174 230 195 39 131 103 188 167 173 231 194 40 130 104 189 168 172 232 193 41 129 105 190 169 171 233 192 42 128 106 191 170 170 234 191 43 128 107 192 171 171 235 190 44 129 108 193 172 172 236 189 45 130 109 194 173 173 237 188 46 131 110 195 174 174 238 187 47 132 111 196 175 175 239 186 48 133 112 197 176 176 240 185 49 134 113 198 177 177 241 184 50 135 114 199 178 178 242 183 51 136 115 200 179 179 243 182 52 137 116 201 180 180 244 181 53 138 117 202 181 181 245 180 54 139 118 203 182 182 246 179 55 140 119 204 183 183 247 178 56 141 120 205 184 184 248 177 57 142 121 206 185 185 249 176 58 143 122 207 186 186 250 175 59 144 123 208 187 187 251 174 60 145 124 209 188 188 252 173 61 146 125 210 189 189 253 172 62 147 126 211 190 190 254 171 63 148 127 212 191 191 255 170

TABLE 5 THRESHOLD THRESHOLD THRESHOLD THRESHOLD DENSITY VALUE DENSITY VALUE DENSITY VALUE DENSITY VALUE 0 85 64 64 128 85 192 85 1 84 65 65 129 85 193 85 2 83 66 66 130 85 194 85 3 82 67 67 131 85 195 85 4 81 68 68 132 85 196 85 5 80 69 69 133 85 197 85 6 79 70 70 134 85 198 85 7 78 71 71 135 85 199 85 8 77 72 72 136 85 200 85 9 76 73 73 137 85 201 85 10 75 74 74 138 85 202 85 11 74 75 75 139 85 203 85 12 73 76 76 140 85 204 85 13 72 77 77 141 85 205 85 14 71 78 78 142 85 206 85 15 70 79 79 143 85 207 85 16 69 80 80 144 85 208 85 17 68 81 81 145 85 209 85 18 67 82 82 146 85 210 85 19 66 83 83 147 85 211 85 20 65 84 84 148 85 212 85 21 64 85 85 149 85 213 85 22 63 86 85 150 85 214 85 23 62 87 85 151 85 215 85 24 61 88 85 152 85 216 85 25 60 89 85 153 85 217 85 26 59 90 85 154 85 218 85 27 58 91 85 155 85 219 85 28 57 92 85 156 85 220 85 29 56 93 85 157 85 221 85 30 55 94 85 158 85 222 85 31 54 95 85 159 85 223 85 32 53 96 85 160 85 224 85 33 52 97 85 161 85 225 85 34 51 98 85 162 85 226 85 35 50 99 85 163 85 227 85 36 49 100 85 164 85 228 85 37 48 101 85 165 85 229 85 38 47 102 85 166 85 230 85 39 46 103 85 167 85 231 85 40 45 104 85 168 85 232 85 41 44 105 85 169 85 233 85 42 43 106 85 170 85 234 85 43 43 107 85 171 85 235 85 44 44 108 85 172 85 236 85 45 45 109 85 173 85 237 85 46 46 110 85 174 85 238 85 47 47 111 85 175 85 239 85 48 48 112 85 176 85 240 85 49 49 113 85 177 85 241 85 50 50 114 85 178 85 242 85 51 51 115 85 179 85 243 85 52 52 116 85 180 85 244 85 53 53 117 85 181 85 245 85 54 54 118 85 182 85 246 85 55 55 119 85 183 85 247 85 56 56 120 85 184 85 248 85 57 57 121 85 185 85 249 85 58 58 122 85 186 85 250 85 59 59 123 85 187 85 251 85 60 60 124 85 188 85 252 85 61 61 125 85 189 85 253 85 62 62 126 85 190 85 254 85 63 63 127 85 191 85 255 85

TABLE 6 THRESHOLD THRESHOLD THRESHOLD THRESHOLD DENSITY VALUE DENSITY VALUE DENSITY VALUE DENSITY VALUE 0 170 84 170 128 170 192 170 1 170 65 170 129 170 193 170 2 170 66 170 130 170 194 170 3 170 67 170 131 170 195 170 4 170 68 170 132 170 196 170 5 170 69 170 133 170 197 170 6 170 70 170 134 170 198 170 7 170 71 170 135 170 199 170 8 170 72 170 136 170 200 170 9 170 73 170 137 170 201 170 10 170 74 170 138 170 202 170 11 170 75 170 139 170 203 170 12 170 76 170 140 170 204 170 13 170 77 170 141 170 205 170 14 170 78 170 142 170 206 170 15 170 79 170 143 170 207 170 16 170 80 170 144 170 208 170 17 170 81 170 145 170 209 170 18 170 82 170 146 170 210 170 19 170 83 170 147 170 211 170 20 170 84 170 148 170 212 170 21 170 85 170 149 170 213 170 22 170 86 170 150 170 214 170 23 170 87 170 151 170 215 170 24 170 88 170 152 170 216 170 25 170 89 170 153 170 217 170 26 170 90 170 154 170 218 170 27 170 91 170 155 170 219 170 28 170 92 170 156 170 220 170 29 170 93 170 157 170 221 170 30 170 94 170 158 170 222 170 31 170 95 170 159 170 223 170 32 170 96 170 160 170 224 170 33 170 97 170 161 170 225 170 34 170 98 170 162 170 226 170 35 170 99 170 163 170 227 170 36 170 100 170 164 170 228 170 37 170 101 170 165 170 229 170 38 170 102 170 166 170 230 170 39 170 103 170 167 170 231 170 40 170 104 170 168 170 232 170 41 170 105 170 169 170 233 170 42 170 106 170 170 170 234 170 43 170 107 170 171 170 235 170 44 170 108 170 172 170 236 170 45 170 109 170 173 170 237 170 46 170 110 170 174 170 238 170 47 170 111 170 175 170 239 170 48 170 112 170 176 170 240 170 49 170 113 170 177 170 241 170 50 170 114 170 178 170 242 170 51 170 115 170 179 170 243 170 52 170 116 170 180 170 244 170 53 170 117 170 181 170 245 170 54 170 118 170 182 170 246 170 55 170 119 170 183 170 247 170 56 170 120 170 184 170 248 170 57 170 121 170 185 170 249 170 58 170 122 170 186 170 250 170 59 170 123 170 187 170 251 170 60 170 124 170 188 170 252 170 61 170 125 170 189 170 253 170 62 170 126 170 190 170 254 170 63 170 127 170 191 170 255 170

For example, in a case where the threshold condition processing as shown in FIG. 11A is performed in accordance with the present embodiment, first, at steps S110 to S150, the threshold condition processing as shown in FIG. 11B is performed, then at steps S160 to S200, the threshold condition processing as shown in FIG. 11C is performed.

Similarly, in a case where the threshold condition processing as shown in FIG. 12A is performed in accordance with the present embodiment, first, at steps S110 to S150, the threshold condition processing as shown in FIG. 12B is performed, then at steps S160 to S200, the threshold condition processing as shown in FIG. 12C is performed. Especially, the threshold conditions shown in FIGS. 12A to 12C are effective for improvement in uniformity of halftone image.

Accordingly, in the above-described embodiment, even in ternarization of multivalued image data, as the threshold condition processing is performed by using a predetermined format threshold table, even if the threshold conditions are complicated, the processing can be performed in a simple manner, and as the processing is simple, the complicated threshold condition processing can be performed at a high speed.

Note that in the present embodiment, only ternarization is handled, however, if the ink-jet printer as the image output device is capable of handling quaternary or quinary representation by using drop modulation and same-color various density ink (e.g. thin cyan ink, thick cyan ink, thin magenta ink and thick magenta ink), threshold tables for multivalue error diffusion processing such as quaternarization or quinarization may be generated.

[Third Embodiment]

In the first and second embodiments, the C and M components among the multivalued density data are handled; in the present embodiment, the K component in addition to these components is handled.

FIG. 13 is a flowchart showing the image formation control according to the third embodiment of the present invention.

Hereinbelow, the feature of the present embodiment will be described with reference to the flowchart.

First, at step S210, the density values Ct, Mt and Kt of the C, M and K components of pixel of interest are obtained. Next, at step S220, a threshold value (C threshold) used in error diffusion of the C component is obtained based on the obtained M and K component density values Mt and Kt. More specifically, in this embodiment, a threshold table as shown in Table 7 is prepared in the HDD 2002 or the DRAM 1003 of the host device 52 in advance, and the threshold value is determined by referring to the threshold table.

At step S230, the threshold value (C threshold) obtained at step S220 is compared with the density value Ct of the pixel of interest. If Ct≧C threshold holds, the process proceeds to step S240, at which setting is made for printing with the C ink. Thereafter, the process proceeds to step S250. On the other hand, if Ct<C threshold holds at step S230, process skips step S240 and proceeds to step S250.

At step S250, a threshold value (M threshold) used in error diffusion of the M component is obtained based on the obtained C and K component density values Ct and Kt. More specifically, in this embodiment, a threshold table as shown in Table 7 is prepared in the HDD 2002 or the DRAM 1003 of the host device 52 in advance, and the threshold value is determined by referring to the threshold table.

At step S260, the threshold value (M threshold) obtained at step S250 is compared with the density value Mt of the pixel of interest. If Mt≧M threshold holds, the process proceeds to step S270, at which setting is made for printing with the M ink. Thereafter, the process proceeds to step S280. On the other hand, if Mt<M threshold holds at step S260, the process skips step S270 and proceeds to step S280.

Further, at step S280, a threshold value (K threshold) used in error diffusion of the K component is obtained based on the obtained C and M component density values Ct and Mt. More specifically, in this embodiment, a threshold table as shown in Table 7 is prepared in the HDD 2002 or the DRAM 1003 of the host device 52 in advance, and the threshold value is determined by referring to the threshold table.

Accordingly, in this embodiment, the threshold table in Table 7 is commonly used for the C component, the M component and the K component.

At step S290, the threshold value (K threshold) obtained at step S280 is compared with the density value Kt of the pixel of interest. If Kt≧K threshold holds, the process proceeds to step S300, at which setting is made for printing with K ink. Then, the process ends. On the other hand, if Kt<K threshold holds, the process skips step S300 and the process ends.

The code representing the core part of the above processing is as follows.

Ct=C+Cerr Mt=M+Merr Kt=K+Kerr Cthreshold=C₋Threshold₋Table [Mt+Kt] If (Ct>=Cthreshold) Print C Mthreshold=M₋Threshold₋Table [Ct+Kt] If (Mt>=Mthreshold) Print M Kthreshold=M₋Threshold₋Table [Ct+Mt] If (Kt>=Kthreshold) Print K

By executing the above processing, the threshold condition processing for three components, which is complicated in the conventional art as explained by using program code, can easily be performed only by defining a threshold table having a common format and setting different values in the threshold table.

Table 7 is a threshold table commonly used for the C, M and K components.

TABLE 7 THRESHOLD THRESHOLD THRESHOLD THRESHOLD DENSITY VALUE DENSITY VALUE DENSITY VALUE DENSITY VALUE 0 128 84 64 128 128 192 128 1 127 65 65 129 128 193 128 2 126 66 66 130 128 194 128 3 125 67 67 131 128 195 128 4 124 68 68 132 128 196 128 5 123 69 69 133 128 197 128 6 122 70 70 134 128 198 128 7 121 71 71 135 128 199 128 8 120 72 72 136 128 200 128 9 119 73 73 137 128 201 128 10 118 74 74 138 128 202 128 11 117 75 75 139 128 203 128 12 116 76 76 140 128 204 128 13 115 77 77 141 128 205 128 14 114 78 78 142 128 206 128 15 113 79 79 143 128 207 128 16 112 80 80 144 128 208 128 17 111 81 81 145 128 209 128 18 110 82 82 146 128 210 128 19 109 83 83 147 128 211 128 20 108 84 84 148 128 212 128 21 107 85 85 149 128 213 128 22 106 86 86 150 128 214 128 23 105 87 87 151 128 215 128 24 104 88 88 152 128 216 128 25 103 89 89 153 128 217 128 26 102 90 90 154 128 218 128 27 101 91 91 155 128 219 128 28 100 92 92 156 128 220 128 29 99 93 93 157 128 221 128 30 98 94 94 158 128 222 128 31 97 95 95 159 128 223 128 32 96 96 96 160 128 224 128 33 95 97 97 161 128 225 128 34 94 98 98 162 128 226 128 35 93 99 99 163 128 227 128 36 92 100 100 164 128 228 128 37 91 101 101 165 128 229 128 38 90 102 102 166 128 230 128 39 89 103 103 167 128 231 128 40 88 104 104 168 128 232 128 41 87 105 105 169 128 233 128 42 86 106 106 170 128 234 128 43 85 107 107 171 128 235 128 44 84 108 108 172 128 236 128 45 83 109 109 173 128 237 128 46 82 110 110 174 128 238 128 47 81 111 111 175 128 239 128 48 80 112 112 176 128 240 128 49 79 113 113 177 128 241 128 50 78 114 114 178 128 242 128 51 77 115 115 179 128 243 128 52 76 116 116 180 128 244 128 53 75 117 117 181 128 245 128 54 74 118 118 182 128 246 128 55 73 119 119 183 128 247 128 56 72 120 120 184 128 248 128 57 71 121 121 185 128 249 128 58 70 122 122 188 128 250 128 59 69 123 123 187 128 251 128 60 68 124 124 188 128 252 128 61 67 125 125 189 128 253 128 62 66 126 126 190 128 254 128 63 65 127 127 191 128 255 128

Accordingly, in the above-described embodiment, as the threshold conditional processing is performed by using a predetermined format threshold table, even the error diffusion processing handling three components with complicated threshold conditions can be performed in a simple manner, and as the processing is simple, the complicated threshold condition processing can be performed at a high speed.

Further, if the present embodiment is combined with the ternarization processing of the second embodiment, the advantages of simplification and increase in processing speed can be further improved.

Note that the present invention is not limited to the threshold tables described in the above-described embodiments. If the format of the threshold table is maintained while the values set in the table are changed, processing can be performed with various threshold conditions as follows.

-   (1) instead of the sum of the C and M component density values     (C+M), threshold conditions such as the sum of squares of the C and     M component density values (C²+M²) are employed. Table 8 is a     threshold table used in this case.

TABLE 8 THRESHOLD THRESHOLD THRESHOLD THRESHOLD DENSITY VALUE DENSITY VALUE DENSITY VALUE DENSITY VALUE 0 128 64 110 128 128 192 143 1 127 65 110 129 129 193 143 2 127 66 109 130 130 194 142 3 127 67 109 131 131 195 141 4 127 68 108 132 132 196 141 5 127 69 107 133 133 197 140 6 127 70 107 134 134 198 140 7 127 71 106 135 135 199 139 8 127 72 105 136 136 200 139 9 127 73 105 137 137 201 138 10 127 74 104 138 138 202 138 11 127 75 103 139 139 203 138 12 127 76 102 140 140 204 137 13 127 77 102 141 141 205 137 14 127 78 101 142 142 206 136 15 127 79 100 143 143 207 138 16 126 80 99 144 144 208 135 17 126 81 99 145 145 209 135 18 126 82 98 146 146 210 135 19 126 83 97 147 147 211 134 20 126 84 96 148 148 212 134 21 126 85 95 149 149 213 134 22 126 86 94 150 150 214 133 23 125 87 93 151 151 215 133 24 125 88 92 152 152 216 133 25 125 89 91 153 153 217 132 26 125 90 91 154 154 218 132 27 125 91 91 155 155 219 132 28 124 92 92 156 156 220 131 29 124 93 93 157 157 221 131 30 124 94 94 158 158 222 131 31 124 95 95 159 159 223 131 32 123 96 96 160 160 224 130 33 123 97 97 161 161 225 130 34 123 98 98 162 162 226 130 35 123 99 99 163 163 227 130 36 122 100 100 164 164 228 129 37 122 101 101 165 163 229 129 38 122 102 102 166 163 230 129 39 121 103 103 167 162 231 129 40 121 104 104 168 161 232 129 41 121 105 105 169 160 233 128 42 120 106 106 170 159 234 128 43 120 107 107 171 158 235 128 44 120 108 108 172 157 236 128 45 119 109 109 173 156 237 128 46 119 110 110 174 155 238 128 47 119 111 111 175 155 239 128 48 118 112 112 176 154 240 127 49 118 113 113 177 153 241 127 50 117 114 114 178 152 242 127 51 117 115 115 179 152 243 127 52 116 116 116 180 151 244 127 53 116 117 117 181 150 245 127 54 116 118 118 182 149 246 127 55 115 119 119 183 149 247 127 56 115 120 120 184 148 248 127 57 114 121 121 185 147 249 127 58 114 122 122 186 147 250 127 59 113 123 123 187 146 251 127 60 113 124 124 188 145 252 127 61 112 125 125 189 145 253 127 62 111 126 126 190 144 254 127 63 111 127 127 191 144 255 127

In a case where an ink-jet printer having a slightly greater ink discharge amount is used as the image output device, isolated dots formed by the C or M ink are easily recognized in a very low density image area, and the uniformity of the image is impaired by exclusive arrangement of these dots, if the above threshold conditions are used, the correlation between the C component and the M component can be slightly lowered and the uniformity of the image can be maintained.

-   (2) As shown in FIG. 9B, threshold conditions overlapped with noise     are employed. Table 9 is a threshold table used in this case.

TABLE 9 THRESHOLD THRESHOLD THRESHOLD THRESHOLD DENSITY VALUE DENSITY VALUE DENSITY VALUE DENSITY VALUE 0 130 64 66 128 130 192 193 1 127 65 65 129 129 193 190 2 124 66 64 130 128 194 187 3 125 67 67 131 131 195 188 4 126 68 70 132 134 196 189 5 123 69 69 133 133 197 186 6 120 70 68 134 132 198 183 7 121 71 71 135 135 199 184 8 122 72 74 136 138 200 185 9 119 73 73 137 137 201 182 10 116 74 72 138 136 202 179 11 117 75 75 139 139 203 180 12 116 76 78 140 142 204 181 13 115 77 77 141 141 205 178 14 112 78 76 142 140 206 175 15 113 79 79 143 143 207 176 16 114 80 82 144 148 208 177 17 111 81 81 145 145 209 174 18 108 82 80 146 144 210 171 19 109 83 83 147 147 211 172 20 110 84 86 148 150 212 173 21 107 85 85 149 149 213 170 22 104 86 84 150 148 214 167 23 105 87 87 151 151 215 168 24 106 88 90 152 154 216 169 25 103 89 89 153 153 217 166 26 100 90 88 154 152 218 163 27 101 91 91 155 155 219 164 28 102 92 94 156 158 220 165 29 99 93 93 157 157 221 162 30 96 94 92 158 156 222 159 31 97 95 95 159 159 223 160 32 98 96 98 160 162 224 161 33 95 97 97 161 161 225 158 34 92 98 96 162 160 226 155 35 93 99 99 163 163 227 156 36 94 100 102 164 166 228 157 37 91 101 101 165 165 229 154 38 88 102 100 166 164 230 151 39 89 103 103 167 167 231 152 40 90 104 106 168 170 232 153 41 87 105 105 169 169 233 150 42 84 106 104 170 168 234 147 43 85 107 107 171 171 235 148 44 86 108 110 172 174 236 149 45 83 109 109 173 173 237 146 46 80 110 108 174 172 238 143 47 81 111 111 175 175 239 144 48 82 112 114 176 178 240 145 49 79 113 113 177 177 241 142 50 76 114 112 178 176 242 139 51 77 115 115 179 179 243 140 52 78 116 118 180 182 244 141 53 75 117 117 181 181 245 138 54 72 118 116 182 180 246 135 55 73 119 119 183 183 247 136 56 74 120 122 184 186 248 137 57 71 121 121 185 185 249 134 58 68 122 120 186 184 250 131 59 69 123 123 187 187 251 132 60 70 124 126 188 190 252 133 61 67 125 125 189 189 253 130 62 64 126 124 190 188 254 127 63 65 127 127 191 191 255 128

By using the threshold conditions, the probability of formation of continuous C-ink or M-ink dots can be reduced.

-   (3) As shown in FIG. 9C, the tendency of error diffusion is changed     in a highlight area and intermediate to high density areas. By using     the threshold conditions, the degradation of image quality due to     fluctuation of ink dot application position can be reduced. -   (4) As shown in FIG. 9D, the boundaries of thresholds are smoothed     as much as possible. By using such threshold conditions, the abrupt     change can be reduced between an area where C and N inks are     exclusively used and an area where the C and M inks are not     exclusively used, and capability of representing an image can be     improved.

In this manner, the threshold condition processing has flexibility by use of a threshold table. If the threshold table is used in combination with actual ink discharge amount or ink composition in the ink-jet printer, the content of image formation processing and/or purpose of the processing can be easily changed.

[Fourth Embodiment]

Further, assume that the ink-jet printer IJRA can handle multivalued image data by using drop modulation and/or same-color thick and thin inks (e.g., thin cyan ink, thick cyan ink, thin magenta ink and thick magenta ink).

In the present embodiment, unlike the conventional art, multivalued density data is ternarized by the error diffusion processing. The data handled by the error diffusion processing according to this embodiment is C component and M component multivalued image data.

FIG. 14 is a flowchart showing the image formation control according to the fourth embodiment of the present invention.

Hereinbelow, the feature of the present embodiment will be described with reference to the flowchart.

First, at step S310, the density values Ct and Mt of the C and M components of pixel of interest are obtained as in the case of the conventional art. Next, at step S320, it is determined whether or not the sum of the obtained M component density value Mt and the C component density value Ct is greater than a first threshold value (Threshold1). If Ct+Mt>Threshold1 holds, the process proceeds to step S330, at which it is determined whether or not the sum of the M component density value Mt and the C component density value Ct is less than a second threshold value (Threshold2). On the other hand, if Ct+Mt≦Threshold1 holds at step S320, the process ends.

At step S330, if Ct+Mt<Threshold2 holds, the process proceeds to step S340, at which the M component density value Mt and the C component density value Ct are compared with each other. If Ct>Mt holds, the process proceeds to step S350, at which setting is made for printing with small-sized C ink droplet (or thin C ink). On the other hand, if Ct≦Mt holds, the process proceeds to step S360, at which setting is made for printing with small-sized M ink droplet (or thin M ink). After step S350 or S360, the process ends.

At step S330, if Ct+Mt≧Threshold2 holds, the process proceeds to step S370, at which it is determined whether or not the sum of the M component density value Mt and the C component density value Ct is less than a third threshold value (Threshold3). If Ct+Mt<Threshold3 holds, the process proceeds to step S380, at which it is determined whether or not the difference between the M component density value Mt and the C component density value Ct is greater than a predetermined offset value (Offset1). If Ct−Mt>Offset1 holds, the process proceeds to step S390, at which setting is made for printing with large-sized C ink droplet (or thick C ink). Then, the process ends. On the other hand, if Ct−Mt≦Offset1 holds, the process proceeds to step S400.

At step S400, it is determined whether or not the difference between the M component density value Mt and the C component density value Ct is greater than a predetermined offset value (Offset2). If Mt−Ct≦Offset2 holds, the process proceeds to step S410, at which setting is made for printing with small-sized C ink droplet (or thin C ink) and small-sized M ink droplet (or thin M ink). Then, the process ends. On the other hand, if Mt−Ct>Offset2 holds, the process proceeds to step S420, at which setting is made for printing with large-sized M ink droplet (or thick M ink). Then, the process ends.

Further, at step S370, if Ct+Mt≧Threshold3 holds, the process proceeds to step S430, at which it is determined whether or not the sum of the M component density value Mt and the C component density value Ct is less than a fourth threshold value (Threshold4). If Ct+Mt<Threshold4 holds, the process proceeds to step S440, at which the M component density value Mt and the C component density value Ct are compared with each other. If Ct>Mt holds, the process proceeds to step S450, at which setting is made for printing with large-sized C ink droplet (or thick C ink) and small-sized M ink droplet (or thin M ink). Then the process ends. On the other hand, if Ct≦Mt holds, the process proceeds to step S460, at which setting is made for printing with small-sized C ink droplet (or thin C ink) and large-sized M ink droplet (or thick M ink). Then, the process ends.

On the other hand, at step S430, if Ct+Mt≧Threshold4 holds, the process proceeds to step S470, at which setting is made for printing with large-sized C ink droplet (or thick C ink) and large-sized M ink droplet (or thick M ink). Then, the process ends.

FIG. 15 shows the threshold conditions for the C and M components in the processing shown in FIG. 14.

In the above-described processing, the following dot arrangements are made in accordance with the M component density value Mt and the C component density value Ct.

-   (1) Ct+Mt≦Threshold1

(C and M components belong to low density area→area (a) in FIG. 15)

Dot printing is not performed.

-   (2) Ct+Mt>Threshold1 and Ct+Mt<Threshold2 and Ct>Mt

(C component belongs to intermediate density area→area (b) in FIG. 15)

Dot printing with small-sized C ink droplet (or thin C ink)(exclusive printing).

-   (3) Ct+Mt>Threshold1 and Ct+Mt<Threshold2 and Ct≦Mt

(M component belongs to intermediate density area→area (c) in FIG. 15)

Dot printing with small-sized M ink droplet (or thin M ink)(exclusive printing).

-   (4) Ct+Mt>Threshold1 and Ct+Mt≧Threshold2 and Ct+Mt<Threshold3 and     Ct−Mt>Offset1

(C component belongs to high density area→area (d) in FIG. 15)

Dot printing with large-sized C ink droplet (or thick C ink)(exclusive printing).

-   (5) Ct+Mt>Threshold1 and Ct+Mt≧Threshold2 and Ct+Mt<Threshold3 and     Ct−Mt≦Offset1 and Mt−Ct≦Offset2

(C and M components belong to intermediate density area→area (e) in FIG. 15)

Dot printing with small-sized C ink droplet (or thin C ink) and small-sized M ink droplet (or thin M ink) (overlay printing).

-   (6) Ct+Mt>Threshold1 and Ct+Mt≧Threshold2 and Ct+Mt<Threshold3 and     Mt−Ct≦Offset1 and Mt−Ct>Offset2

(M component belongs to high density area→area (f) in FIG. 15)

Dot printing with large-sized M ink droplet (or thick M ink) (exclusive printing).

-   (7) Ct+Mt>Threshold1 and Ct+Mt≧Threshold2 and Ct+Mt≧Threshold3 and     Ct+Mt<Threshold4 and Ct>Mt

(C component belongs to high density area and M component belongs to intermediate density area→area (g) in FIG. 15)

Dot printing with large-sized C ink droplet (or thick C ink) and small-sized M ink droplet (or thin M ink)(overlay printing).

-   (8) Ct+Mt>Threshold1 and Ct+Mt≧Threshold2 and Ct+Mt≧Threshold3 and     Ct+Mt<Threshold4 and Ct≦Mt

(C component belongs to intermediate density area and M component belongs to high density area→area (h) in FIG. 15)

Dot printing with small-sized C ink droplet (or thin C ink) and large-sized M ink droplet (or thick M ink) (overlay printing).

-   (9) Ct+Mt≧Threshold4 (>Threshold3>Threshold2>Threshold1)

(C and M components belong to high density area→area (i) in FIG. 15)

Dot printing with large-sized C ink droplet (or thick C ink) and large-sized M ink droplet (or thick M ink) (overlay printing).

Accordingly, in the above-described present embodiment, as the printing with the M ink and C ink is changed in accordance with the C component and M component density values, printing with reduced graininess can be performed by ternarizing the C component and M component density values and exclusively arranging printed dots based on the ternarization.

[Fifth Embodiment]

In the fourth embodiment, the multivalued density data is ternarized by the error diffusion processing; in the present embodiment, an example of high-speed processing in consideration of conversion of multivalued density data into N-ary code (N≧4) by the error diffusion will be described.

As it is apparent from the flowchart of FIG. 14 described in the first embodiment, in the case of ternarization, the C and M components are respectively ternarized, 9 (=3×3) arrangements are considered and branching processings by 8 “if” statements (condition statements) are required. That is, in the case of converting into N-ary code, N²−1 “if” statements are required. Accordingly, as the value of N increases, processing time increases.

FIG. 16 is a flowchart showing the image formation control according to the fifth embodiment of the present invention.

Hereinbelow, the feature of the present embodiment will be described with reference to the flowchart.

In the present embodiment, as the threshold condition processing is very complicated in the conversion of input multivalued image data into N-ary code (N≧3) by the error diffusion processing, the conversion is made by the following procedure.

(1) Functions defined as X=Ct+Mt and Y=Ct−Mt are introduced for execution of multivalue error diffusion.

(2) A two-dimensional table is referred to based on the result of multivalue error diffusion processing, so as to determine arrangement of dots to be printed and dot type. The two-dimensional table may be a common table for the C and M components, however, actually, it is preferable that tables (C_Table and M_Table) respectively for the C and M components are prepared.

Returning to FIG. 16, first, at step S510, X and Y values are determined from density values of the C and M components in each pixel.

Next, at step S520, arguments (X_index, Y_index) of the above-described two-dimensional table are determined based on the X and Y values. In this embodiment, the arguments are determined as X and Y functions (X_index=f(X), Y_index=g(Y)).

Finally, at step S530, the two-dimensional table is referred to by using the arguments determined at step S520, and output values by the error diffusion processing of the C and M components (C out, M out) are determined.

For comparison, an example of ternarization processing the same as that described in the fourth embodiment, in accordance with the present embodiment, will be described.

FIG. 17 shows the ternarization according to the fifth embodiment.

FIG. 17 shows quaternarization of X=Ct(=C+Cerr)+Mt(=M+Merr) and quinarization of Y=Ct(=C+Cerr)−Mt(=M+Merr).

In FIG. 17, a right-upward straight line indicates the same X value (=Ct−Mt), and a left-upward straight line, the same Y value (=Ct+Mt) (Ct and Mt have variation widths of about −128≦Ct, Mt≦383 including error-accumulation).

Accordingly, as the values Ct and Mt have the above variation widths, the X value has a variation width of about −256≦X≦766, and the Y value, a variation width of about −511≦Y≦511. To quaternarize and quinarize the X and Y values having the above variation widths, the function of X (f(X)) and that of Y (g(Y)) are introduced.

That is, X_index=f(X) and Y_index=g(Y) are calculated. The calculations can be realized by referring to the table.

In this manner, two additions and two multivalue conversion calculations (referring to the table) divide the entire X and Y range into quaternary×quinary=20 sections.

In comparison between FIGS. 17 and 15, the areas (a), (b), (c), (e), (g), (h) and (i) in FIG. 15 are respectively 2 sections in FIG. 17. The entire partitioning is approximately common to FIGS. 15 and 17.

Accordingly, print control based on the error-diffusion processing by C and M ternarization can be performed by referring to a common two-dimensional table as shown in FIG. 18 based on the results of X and Y multivalue conversion.

Note that in FIG. 18, “_” means non-execution of dot printing with C or M ink; “c”, dot printing with small-sized C ink droplet (or thin C ink); “m”, dot printing with small-sized M ink droplet (or thin M ink); “C”, dot printing with large-sized C ink droplet (or thick C ink); “M”, dot printing with large-sized M ink droplet (or thick M ink); “cm”, dot printing with small-sized C ink droplet (or thin C ink) and small-sized M ink droplet (or thin M ink); “Cm”, dot printing with large-sized C ink droplet (or thick C ink) and small-sized M ink droplet (or thin M ink); “cM”, dot printing with small-sized C ink droplet (or thin C ink) and large-sized M ink droplet (or thick M ink); and “CM”, dot printing with large-sized C ink droplet (or thick C ink) and large-sized M ink droplet (or thick M ink).

Actually, it is desirable that two-dimensional tables are prepared respectively for the C and M components in consideration of color characteristics of the C and M components, as shown in FIGS. 19A and 19B.

FIG. 19A shows a two-dimensional table specialized for the C component, and FIG. 19B, a two-dimensional table specialized for the M component.

Further, in FIGS. 19A and B, “_” means non-execution of dot printing; “c”, dot printing with small-sized C ink droplet (or thin C ink); “m”, dot printing with small-sized M ink droplet (or thin M ink); “C”, dot printing with large-sized C ink droplet (or thick C ink); and “M”, dot printing with large-sized M ink droplet (or thick M ink).

In the above example, for the sake of simplification of explanation, ternarization has been described, however, in the present embodiment, as conversion into N-ary code (N≧4) can be realized by using simple processing steps without conditional branch processing, i.e., XY calculation, XY multivalue conversion processing and multivalue conversion of the C and M components, the embodiment provides more effective processing for N of the higher-order.

Accordingly, in the above-described present embodiment, regarding conversion into N-ary code of the higher-order, the error diffusion processing can be performed at a high speed without complicated processing.

Further, according to the above-described present embodiment, as the processing is mainly performed with reference to table(s) without calculation accompanied with condition determination, the processing is advantageous in e.g. pipeline processing and/or lookahead processing used in an MPU such as an Pentium compatible processor. If such processor is employed in the present embodiment, higher-speed processing can be expected.

[Sixth Embodiment]

In the present embodiment, the error diffusion processing capable of controlling pixel arrangement by each density component in accordance with density value, different from the error diffusion of the conventional art, will be described. The error diffusion processing according to the present embodiment handles multivalued image data of C and M components.

In the present embodiment, the multivalued density data is binarized by the error-diffusion processing.

FIG. 20 is a flowchart showing the image formation control according to the sixth embodiment of the present invention.

Hereinbelow, the feature of the present embodiment will be described with reference to the flowchart.

First, at step S610, the density values Ct and Mt of the C and M components of pixel of interest are obtained as in the case of the conventional art. Next, at step S620, it is determined whether or not the sum of the obtained M component density value Mt and the C component density value Ct is greater than a density value 127 used as a threshold value. If Ct+Mt>127 holds, the process proceeds to step S630, at which the M component density value Mt and the C component density value Ct are compared with each other.

If Ct>Mt holds, the process proceeds to step S640, at which setting is made for printing with the C ink. Further, at step S650, it is determined whether or not the M component density value Mt is greater than the threshold value 127. If Mt>127 holds, the process proceeds to step S670, at which setting is made for printing with the M ink. Then the process ends. On the other hand, if Mt≦127 holds, the process skips step S670 and the process ends.

At step S630, if Ct≦Mt holds, the process proceeds to step S680, at which setting is made for printing with the M ink. Further, the process proceeds to step S690, at which it is determined whether or not the C component density value Ct is greater than the threshold value 127. If Ct>127 holds, the process proceeds to step S700, at which setting is made for printing with the C ink. Then, the process ends. On the other hand, if Ct≦127 holds, the process skips step S700 and the process ends.

Further, at step S620, if Ct+Mt≦127 holds, the process ends.

FIG. 21 is a diagram showing threshold conditions for the C and M components in the processing shown in FIG. 20.

In the above-described processing, the following dot arrangements are made in accordance with the M component density value Mt and the C component density value Ct.

-   (1) Ct+Mt≦127

(C and M components belong to low density area→area (a) in FIG. 21)

Dot printing is not performed.

-   (2) Ct+Mt>127 and Ct>Mt and Mt>127

(C and M components belong to intermediate to high density area→area (d) in FIG. 21)

Dot printing with C and M inks (overlay printing).

-   (3) Ct+Mt>127 and Ct>Mt and Mt≦127

(only C component belongs to intermediate to high density area→area (b) in FIG. 21)

Dot printing with only C ink (exclusive printing).

-   (4) Ct+Mt>127 and Ct<Mt and Ct>127

(C and M components belong to intermediate to high density area→area (d) in FIG. 21)

Dot printing with C and M inks (overlay printing).

-   (5) Ct+Mt>127 and Ct≦Mt and Ct≦127

(only M component belongs to intermediate to high density area→area (c) in FIG. 21)

Dot printing with only M ink (exclusive printing).

Accordingly, in the above-described embodiment, if only one density component has a sufficiently high density, printing pixels are formed for the color component without depending on another component. Thus, printing independency of the C and M components in intermediate to high density areas is enhanced. Thus the uniformity of image can be maintained in intermediate and higher density areas.

[Seventh Embodiment]

In the sixth embodiment, the multivalued density data is binarized by the error diffusion processing; in the present embodiment, multivalued density data is ternarized by the error diffusion processing.

FIG. 22 is a flowchart showing the image formation control according to the seventh embodiment of the present invention.

Hereinbelow, the feature of the present embodiment will be described with reference to the flowchart.

First, at step S710, the density values Ct and Mt of the C and M components of pixel of interest are obtained as in the case of the conventional art. Next, at step S720, the sum of the obtained M component density value Mt and the C component density value Ct is compared with a threshold value (Threshold). If Ct+Mt>Threshold holds, the process proceeds to step S730, while if Ct+Mt≦Threshold holds, proceeds to step S760.

At step S730, the M component density value Mt and the C component density value Ct are compared with each other. If Ct>Mt holds, the process proceeds to step S740, at which output values by the error diffusion processing of the C and M components are determined.

That is, a common multivalue conversion table for the C and M components as shown in Table 10 is used. First, as the C component output value (C out), a greater one of “1” and f(Ct) value (in multivalue conversion table as a function of a density value Ct) is selected. For example, if f(Ct) is “0”, C out=1 holds; if f(Ct) is “1”, C out=1 holds; and if f(Ct) is “2”, C out=2 holds.

Further, as the M component output value (M out), a value corresponding to the density value Mt is determined by referring to the multivalue conversion table of Table 10, as M out=g(Mt)(in multivalue conversion table as a function of a density value Mt).

TABLE 10 MULTIVALUE MULTIVALUE MULTIVALUE MULTIVALUE OUTPUT OUTPUT OUTPUT OUTPUT DENSITY VALUE DENSITY VALUE DENSITY VALUE DENSITY VALUE 0 0 64 0 128 1 192 2 1 0 65 0 129 1 193 2 2 0 66 0 130 1 194 2 3 0 67 0 131 1 195 2 4 0 68 0 132 1 196 2 5 0 69 0 133 1 197 2 6 0 70 0 134 1 198 2 7 0 71 0 135 1 199 2 8 0 72 0 136 1 200 2 9 0 73 0 137 1 201 2 10 0 74 0 138 1 202 2 11 0 75 0 139 1 203 2 12 0 76 0 140 1 204 2 13 0 77 0 141 1 205 2 14 0 78 0 142 1 206 2 15 0 79 0 143 1 207 2 16 0 80 0 144 1 208 2 17 0 81 0 145 1 209 2 18 0 82 0 146 1 210 2 19 0 83 0 147 1 211 2 20 0 84 0 148 1 212 2 21 0 85 1 149 1 213 2 22 0 86 1 150 1 214 2 23 0 87 1 151 1 215 2 24 0 88 1 152 1 216 2 25 0 89 1 153 1 217 2 26 0 90 1 154 1 218 2 27 0 91 1 155 1 219 2 28 0 92 1 156 1 220 2 29 0 93 1 157 1 221 2 30 0 94 1 158 1 222 2 31 0 95 1 159 1 223 2 32 0 96 1 160 1 224 2 33 0 97 1 161 1 225 2 34 0 98 1 162 1 226 2 35 0 99 1 163 1 227 2 36 0 100 1 164 1 228 2 37 1 101 1 165 1 229 2 38 0 102 1 166 1 230 2 39 0 103 1 167 1 231 2 40 0 104 1 168 1 232 2 41 0 105 1 169 1 233 2 42 0 106 1 170 2 234 2 43 0 107 1 171 2 235 2 44 0 108 1 172 2 236 2 45 0 109 1 173 2 237 2 46 0 110 1 174 2 238 2 47 0 111 1 175 2 239 2 48 0 112 1 176 2 240 2 49 0 113 1 177 2 241 2 50 0 114 1 178 2 242 2 51 0 115 1 179 2 243 2 52 0 116 1 180 2 244 2 53 0 117 1 181 2 245 2 54 0 118 1 182 2 246 2 55 0 119 1 183 2 247 2 56 0 120 1 184 2 248 2 57 0 121 1 185 2 249 2 58 0 122 1 186 2 250 2 59 0 123 1 187 2 251 2 60 0 124 1 188 2 252 2 61 0 125 1 189 2 253 2 62 0 126 1 190 2 254 2 63 0 127 1 191 2 255 2

Further, if Ct≦Mt holds, the process proceeds to step S750, at which the common multivalue conversion table for the C and M components shown in the Table 10 is referred to, and the output values from the error diffusion processing of the C and M components are determined.

That is, as the C component output value (C out), a value corresponding to the density value Ct is determined by referring to the multivalue conversion table of Table 10, as C out=f(Ct), and as the M component output value (M out), a greater one of “1” and g(Mt) value (in multivalue conversion table as a function of a density value Mt) is selected.

Further, at step S760, the common multivalue conversion table for the C and M components shown in the Table 10 is referred to, then, as the C component output value (C out), a value corresponding to the density value Ct is determined by referring to the multivalue conversion table in Table 10, as C out=f(Ct), and as the M component output value (M out), a value corresponding to the density value Mt is determined by referring to the multivalue conversion table of Table 10, as M out=g(Mt).

After steps S740 and S750 or S760, the process ends.

Note that in this embodiment, “85” is used as the threshold value (Threshold).

FIG. 23 is a diagram showing threshold conditions regarding the C and M components in the processing shown in FIG. 22.

Further, in the present embodiment, for the sake of simplification of explanation, a common table is used as the multivalue conversion tables f(Ct) and g(Mt), however, the common table is not necessarily used but separate tables may be used.

Further, Table 10 merely has density values 0 to 255, however, as actual density values Ct and Mt may have density variation widths, which may differ in accordance with conditions of multivalue conversion means and error diffusion method, about −128 to +383 at the maximum, the present invention is not limited to the values shown in Table 10. In the present embodiment, although the following values are not included for the sake of simplification of explanation, actually unshown Ct(Mt) table part of “0” or less may have the same values of those in the Ct(Mt)=0 multivalue conversion table, and unshown Ct(Mt) table part of “255” or more may have the same values of those in the Ct(Mt)=255 multivalue conversion table.

Note that in the present embodiment, only ternarization is handled, however, if the ink-jet printer as the image output device is capable of handling quaternary or quinary representation by using drop modulation and same-color various density ink (e.g. thin cyan ink, thick cyan ink, thin magenta ink and thick magenta ink), threshold tables for multivalue error diffusion processing such as quaternarization or quinarization may be generated.

Accordingly, in the above-described embodiment, even in conversion of multivalued image data into N-ary code, as the processing is performed by using a predetermined format threshold table, even if the threshold conditions are complicated, the processing can be performed in a simple manner, and as the processing is simple, the complicated threshold conditional process can be performed at a high speed.

Note that in the above embodiments, the liquid discharged from the printhead has been described as ink, and the liquid contained in the ink tank has been described as ink. However, the liquid is not limited to ink. For example, the ink tank may contain processed liquid or the like discharged to a print medium to improve fixability or water repellency of a printed image or to increase the image quality.

The embodiments described above have exemplified a printer, which comprises means (e.g., an electrothermal transducer, laser beam generator, and the like) for generating heat energy as energy utilized upon execution of ink discharge, and causes a change in state of an ink by the heat energy, among the ink-jet printers. According to this ink-jet printer and printing method, a high-density, high-precision printing operation can be attained.

As the typical arrangement and principle of the ink-jet printing system, one practiced by use of the basic principle disclosed in, for example, U.S. Pat. Nos. 4,723,129 and 4,740,796 is preferable. The above system is applicable to either one of the so-called on-demand type or a continuous type. Particularly, in the case of the on-demand type, the system is effective because, by applying at least one driving signal, which corresponds to printing information and gives a rapid temperature rise exceeding nucleate boiling, to each of electrothermal transducers arranged in correspondence with a sheet or liquid channels holding a liquid (ink), heat energy is generated by the electrothermal transducer to effect film boiling on the heat acting surface of the printhead, and consequently, a bubble can be formed in the liquid (ink) in one-to-one correspondence with the driving signal. By discharging the liquid (ink) through a discharge opening by growth and shrinkage of the bubble, at least one droplet is formed. If the driving signal is applied as a pulse signal, the growth and shrinkage of the bubble can be attained instantly and adequately to achieve discharge of the liquid (ink) with the particularly high response characteristics.

As the pulse driving signal, signals disclosed in U.S. Pat. Nos. 4,463,359 and 4,345,262 are suitable. Note that further excellent printing can be performed by using the conditions described in U.S. Pat. No. 4,313,124 of the invention which relates to the temperature rise rate of the heat acting surface.

As an arrangement of the printhead, in addition to the arrangement as a combination of discharge nozzles, liquid channels, and electrothermal transducers (linear liquid channels or right angle liquid channels) as disclosed in the above specifications, the arrangement using U.S. Pat. Nos. 4,558,333 and 4,459,600, which disclose the arrangement having a heat acting portion arranged in a flexed region is also included in the present invention. In addition, the present invention can be effectively applied to an arrangement based on Japanese Patent Laid-Open Publication No. 59-123670 which discloses the arrangement using a slot common to a plurality of electrothermal transducers as a discharge portion of the electrothermal transducers, or Japanese Patent Laid-Open No. 59-138461 Publication which discloses the arrangement having an opening for absorbing a pressure wave of heat energy in correspondence with a discharge portion.

Furthermore, as a full line type printhead having a length corresponding to the width of a maximum printing medium which can be printed by the printer, either the arrangement which satisfies the full-line length by combining a plurality of printheads as disclosed in the above specification or the arrangement as a single printhead obtained by forming printheads integrally can be used.

In addition, an exchangeable chip type printhead which can be electrically connected to the apparatus main body and can receive ink from the apparatus main body upon being mounted on the apparatus main body can be employed as well as a cartridge type printhead in which an ink tank is integrally arranged on the printhead itself as described in the above embodiments.

It is preferable to add recovery means for the printhead, preliminary auxiliary means and the like to the above-described construction of the printer of the present invention since the printing operation can be further stabilized. Examples of such means include, for the printhead, capping means, cleaning means, pressurization or suction means, and preliminary heating means using electrothermal transducers, another heating element, or a combination thereof. It is also effective for stable printing to provide a preliminary discharge mode which performs discharge independently of printing.

Furthermore, as a printing mode of the printer, not only a printing mode using only a primary color such as black or the like, but also at least one of a multi-color mode using a plurality of different colors or a full-color mode achieved by color mixing can be implemented in the printer either by using an integrated printhead or by combining a plurality of printheads.

Moreover, in each of the above-mentioned embodiments of the present invention, it is assumed that the ink is a liquid. Alternatively, the present invention may employ an ink which is solid at room temperature or less and softens or liquefies at room temperature, or an ink which liquefies upon application of a use printing signal, since it is a general practice to perform temperature control of the ink itself within a range from 30° C. to 70° C. in the ink-jet system, so that the ink viscosity can fall within a stable discharge range.

In addition, in order to prevent a temperature rise caused by heat energy by positively utilizing it as energy for causing a change in state of the ink from a solid state to a liquid state, or to prevent evaporation of the ink, an ink which is solid in a non-use state and liquefies upon heating may be used. In any case, an ink which liquefies upon application of heat energy according to a printing signal and is discharged in a liquid state, an ink which begins to solidify when it reaches a printing medium, or the like, is applicable to the present invention. In this case, an ink may be situated opposite electrothermal transducers while being held in a liquid or solid state in recess portions of a porous sheet or through holes, as described in Japanese Patent Laid-Open Publication No. 54-56847 or 60-71260. In the present invention, the above-mentioned film boiling method is most effective for the above-mentioned inks.

In addition, the ink-jet printer of the present invention may be used in the form of a copying machine combined with a reader and the like, or a facsimile apparatus having a transmission/reception function in addition to an image output terminal of an information processing apparatus such as a computer.

The present invention can be applied to a system constituted by a plurality of devices (e.g., a host computer, an interface, a reader and a printer) or to an apparatus comprising a single device (e.g., a copy machine or a facsimile apparatus).

Further, the object of the present invention can be also achieved by providing a storage medium (or recording medium) storing software program code for performing the aforesaid processes to a system or an apparatus, reading the program code with a computer (e.g., CPU, MPU) of the system or apparatus from the storage medium, then executing the program. In this case, the program code read from the storage medium realizes the functions according to the embodiments, and the storage medium storing the program code constitutes the invention. Furthermore, besides aforesaid functions according to the above embodiments are realized by executing the program code which is read by a computer, the present invention includes a case where an OS (operating system) or the like working on the computer performs a part or entire processes in accordance with designations of the program code and realizes functions according to the above embodiments.

Furthermore, the present invention also includes a case where, after the program code read from the storage medium is written in a function expansion card which is inserted into the computer or in a memory provided in a function expansion unit which is connected to the computer, CPU or the like contained in the function expansion card or unit performs a part or entire process in accordance with designations of the program code and realizes functions of the above embodiments.

As many apparently widely different embodiments of the present invention can be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the appended claims. 

1. An image processing apparatus for performing error diffusion processing on multivalued image data having plural density components and outputting the result of said error diffusion processing, comprising: first determination means for, upon execution of said error diffusion processing on a first density component among said plural density components, determining a threshold value used in said error diffusion processing based on a density value of a second density component; first error diffusion execution means for executing said error diffusion processing on said first density component based on the threshold value determined by said first determination means; first output means for outputting the result of execution of said error diffusion processing by said first error diffusion execution means; second determination means for, upon execution of said error diffusion processing on said second density component among said plural density components, determining a threshold value used in said error diffusion processing based on a density value of said first density component; second error diffusion execution means for performing said error diffusion processing on said second density component based on the threshold value determined by said second determination means; second output means for outputting the result of execution of said error diffusion processing by said second error diffusion execution means; third determination means for, upon execution of said error diffusion processing on a third density component among said plural density components, determining a threshold value used in said error diffusion processing based on the sum of the density values of said first and second density components; third error diffusion execution means for executing said error diffusion processing on said third density component based on the threshold value determined by said third determination means; and third output means for outputting the result of execution of said error diffusion processing by said third error diffusion execution means, wherein, in a case where said error diffusion processing is performed on said first to third density components, said first determination means determines the threshold value used in said error diffusion processing on said first density component, based on the sum of the density value of said second density component and a density value of said third density component, and said second determination means determines the threshold value used in said error diffusion processing on said second density component, based on the sum of the density value of said first density component and the density value of said third density component.
 2. The apparatus according to claim 1, wherein said first and second determination means use a table showing a relation between density and threshold values, for determining the threshold values.
 3. The apparatus according to claim 1, wherein said first and second determination means respectively determine plural threshold values.
 4. The apparatus according to claim 3, wherein said first and second determination means respectively use plural tables for determining said plural threshold values.
 5. The apparatus according to claim 1, wherein said plural density components are a yellow component, a magenta component, a cyan component and a black component, and said first density component is the cyan component, said second density component is the magenta component, and said third density component is the black component.
 6. The apparatus according to claim 1, further comprising image formation means for inputting the results of execution of said error diffusion processing outputted from said first to third output means and performing image formation.
 7. The apparatus according to claim 6, wherein said image formation means is an ink-jet printer.
 8. The apparatus according to claim 7, wherein said ink-jet printer has an ink-jet printhead that discharges ink by utilizing thermal energy, and wherein said ink-jet printhead has electrothermal transducers for generating the thermal energy to be supplied to the ink.
 9. An image processing method for performing error diffusion processing on multivalued image data having plural density components and outputting the result of said error diffusion processing, comprising: a first determination step of, upon execution of said error diffusion processing on a first density component among said plural density components, determining a threshold value used in said error diffusion processing based on a density value of a second density component; a first error diffusion execution step of executing said error diffusion processing on said first density component based on the threshold value determined at said first determination step; a first output step of outputting the result of execution of said error diffusion processing at said first error diffusion execution step; a second determination step of, upon execution of said error diffusion processing on said second density component among said plural density components, determining a threshold value used in said error diffusion processing based on a density value of said first density component; a second error diffusion execution step of performing said error diffusion processing on said second density component based on the threshold value determined at said second determination step; and a second output step of outputting the result of execution of said error diffusion processing at said second error diffusion execution step; a third determination step of, upon execution of said error diffusion processing on a third density component among said plural density components, determining a threshold value used in said error diffusion processing based on the sum of the density values of said first and second density components; a third error diffusion execution step of executing said error diffusion processing on said third density component based on the threshold value determined at said third determination step; and a third output step of outputting the result of execution of said error diffusion processing at said third error diffusion execution step, wherein, in a case where said error diffusion processing is performed on said first to third density components, at said first determination step, the threshold value used in said error diffusion processing on said first density component is determined, based on the sum of the density value of said second density component and a density value of said third density component, and at said second determination step, the threshold value used in said error diffusion processing on said second density component is determined, based on the sum of the density value of said first density component and the density value of said third density component.
 10. The method according to claim 9, wherein at said first and second determination steps, a table showing a relation between density and threshold values is used for determining the threshold values.
 11. The method according to claim 9, wherein at said first and second determination steps plural threshold values are respectively determined.
 12. The method according to claim 11, wherein at said first and second determination steps, plural tables are respectively used for determining said plural threshold values.
 13. A computer readable memory for storing a program for executing the image processing method according to any one of claims 9 to
 12. 